1. Field of the Invention
The present invention relates to an inkjet printhead. More particularly, the present invention relates to a piezoelectric inkjet printhead having an improved structure for preventing cross-talk when ink is ejected, and a method of manufacturing the piezoelectric inkjet printhead.
2. Description of the Related Art
An inkjet printer is a device for forming an image on a medium by ejecting ink droplets onto a desired region of the medium. Inkjet printheads can be classified into two types according to the ejecting mechanism of ink droplets: a thermal type inkjet printhead that creates bubbles by heating the ink to eject ink droplets by the expansion of the bubbles, and a piezoelectric type inkjet printhead that includes a piezoelectric material to eject ink droplets by the pressure generated by the deformation of the piezoelectric material.
FIG. 1 illustrates a structure of a conventional piezoelectric inkjet printhead. Referring to FIG. 1, a manifold 2, a restrictor 3, a pressure chamber 4, and a nozzle 5 are formed in an ink flow plate 1 to form an ink path. A piezoelectric actuator 6 is installed on top of the ink flow plate 1. The manifold 2 supplies ink from an ink reservoir (not shown) to each pressure chamber 4. The restrictor 3 is an ink passage between the manifold 2 and the pressure chamber 4. The pressure chamber 4 receives the ink to be ejected and changes its volume in response to the operation of the piezoelectric actuator 6 to create a pressure variation for ejecting and receiving the ink. A top wall of the pressure chamber 4 deforms and returns to its original shape according to the operation of the piezoelectric actuator 6. The top wall is used as a vibration plate 1a. 
When the vibration plate 1a is deformed by the piezoelectric actuator 6, the volume of the pressure chamber 4 decreases and the pressure of the pressure chamber 4 increases, such that ink contained in the pressure chamber 4 can be ejected through the nozzle 5. When the vibration plate 1a returns to its original shape according to the operation of the piezoelectric actuator 6, the volume of the pressure chamber 4 increases and the pressure of the pressure chamber 4 decreases, such that ink can be supplied to the pressure chamber 4 from the manifold 2 through the restrictor 3.
In the conventional inkjet printhead, the ink flow plate 1 is generally formed of a plurality of thin ceramic, metal, or synthetic plates. The thin plates are individually processed to have shapes corresponding to the ink flow path of the ink flow plate 1, and then the thin plates are stacked and bonded to form the ink flow plate 1. Since the plurality of thin plates is aligned through many operations, alignment errors increase and the manufacturing process of the inkjet printhead is complicated. The alignment errors cause non-smooth ink flow and lower the ink ejecting performance of the inkjet printhead. Particularly, since recent printheads have a highly integrated structure for high resolution, precise aligning becomes more important in the manufacturing process of the printhead. The precise aligning may increase the price of the printhead.
In addition, since the thin plates of the printhead are formed of different materials using different methods, the manufacturing process of the printhead is complicated and it is difficult to bond the thin plates, thereby decreasing the yield of the printhead. Further, since the thin plates of the printhead are formed of different materials, the alignment of the thin plates may be distorted or the thin plates may be deformed according to temperature changes due to different thermal expansion characteristics of the thin plates, even if the thin plates are precisely aligned and bonded together in manufacturing process.
One solution is a piezoelectric inkjet printhead illustrated in FIGS. 2 and 3. Referring to FIGS. 2 and 3, the piezoelectric inkjet printhead has a stacked structure formed by stacking and bonding three silicon substrates 30, 40 and 50.
An upper substrate 30 includes pressure chambers 32 formed in a bottom surface to a predetermined depth and an ink inlet 31 formed through one side for connection with an ink reservoir (not shown). The pressure chambers 32 are arranged in two lines along both sides of a manifold 41 formed in a middle substrate 40. Piezoelectric actuators 60 are formed on a top surface of the upper substrate 30 to apply driving forces to the pressure chambers 32 for ejecting ink. A vibrating plate 33 above the pressure chambers 32 is deformed by the operation of the piezoelectric actuators 60.
The middle substrate 40 includes the manifold 41 connected with the ink inlet 31 and a plurality of restrictors 42 formed on both sides of the manifold 41 in connection with the respective pressure chambers 32. A barrier rib 44 is formed in the manifold 41 to prevent cross-talk between the pressure chambers 32 arranged in two lines along both sides of the manifold 41. The middle substrate 40 further includes dampers 43 formed therethrough in a vertical direction at positions corresponding to the pressure chambers 32 formed in the upper substrate 30.
A lower substrate 50 includes nozzles 51 connected with the dampers 43.
As described above, the piezoelectric inkjet printhead shown in FIGS. 2 and 3 is configured by stacking the three substrates 30, 40, and 50. Thus, since the number of the substrates of the piezoelectric inkjet printhead shown in FIGS. 2 and 3 is less than that of the conventional piezoelectric inkjet printhead, the manufacturing process of the piezoelectric inkjet printhead is simpler and the aligning errors are reduced when the substrates are stacked.
However, when the vibrating plate 33 above the pressure chambers 32 is deformed by the operation of the piezoelectric actuators 60, to eject ink through the nozzles 51, the ink simultaneously flows into the manifold 41 through the restrictors 42. Due to this reverse flow of the ink, the pressure in the manifold 41 may increase non-uniformly. When the vibrating plate 33 returns to its original shape, the ink contained in the manifold 41 may suddenly flow into the pressure chambers 32 through the restrictors 42. Thus, the pressure of the manifold 41 may decrease non-uniformly.
When the pressure inside the manifold 41 changes suddenly and non-uniformly as described above, the pressure chambers 32 adjacent to the manifold 41 are affected by the pressure change of the manifold 41, thereby causing cross-talk between the pressure chambers 32. Meanwhile, although the barrier rib 44 formed in the manifold 41 can prevent cross-talk between the two pressure chamber lines arranged along both sides of the manifold 41, the barrier rib 44 cannot prevent cross-talk between the pressure chambers 32 within each pressure chamber line. If cross-talk occurs when ink is ejected as described above, ink ejecting speed and volumes of ink droplets vary undesirably.
FIG. 4 illustrates speed of ink ejected through a single nozzle in comparison with speed of ink ejected through a plurality of nozzles in the piezoelectric inkjet printhead depicted in FIGS. 2 and 3.
Referring to FIG. 4, when ink is ejected through a single nozzle, as shown in the left side of FIG. 4, the ejected ink droplet reaches a desired position indicated by a solid line since cross-talk between nozzles does not occur almost at all. However, when ink is ejected through a plurality of nozzles, as shown in the right side of FIG. 4, the ejected ink droplets do not reach a desired position indicated by a solid line due to cross-talk between the nozzles. That is, the ink ejecting speed of a single nozzle is different from the ink ejecting speed of a plurality of nozzles.
As described above, if cross-talk occurs when ink is ejected, ink cannot be ejected uniformly, thus decreasing printing quality.